This invention relates to environmentally acceptable stabilized vinyl chloride polymer compositions from which arsenic, cadmium, lead, mercury, and thallium are substantially excluded, and to an anti-yellowing additive so such environmentally acceptable stabilized vinyl chloride polymer compositions to minimize undesirable yellowing during the process of fabricating and shaping such compositions into useful articles.
There is a voluminous literature on the stabilization of vinyl chloride polymers. Patent disclosures of materials stated to be useful in minimizing deterioration of vinyl chloride polymers on heating number well over one thousand. Among the more important heat stabilizers in commercial use are mild alkalis such as sodium carbonate, disodium phosphate, and sodium and potassium salts of partially esterified phosphoric acids; carboxylates and phenolates of zinc, cadmium, and the alkaline earth metals; inorganic and organic lead salts; organotin carboxylates. as disclosed by Quattlebaum in U.S. Pat. No. 2,307,157; organotin mercaptides as disclosed by Leistner in U.S. Pat. Nos. 2,641,588 and 2,641,598; various metal-free organic compounds such as the polyols, e.g. mannitol, sorbitol, glycerol, pentaerythritol, organic phosphites, 1,2-epoxides, e.g., soybean oil epoxide, isooctyl epoxy-stearate, and diglycidyl ether of 2,2-bis(p-hydroxyphenyl) propane, and nitrogen compounds, e.g., phenylurea, N, N'-diphenylthiourea, and 2-phenylindole. For detailed discussion of heat stabilizers for vinyl halide resins, reference may be made to the articles, L. I. Nass, in "Encyclopedia of Polymer Science and Technology" (N. Bikales, ed.) Vol. 12, pages 737 to 768 (1970); N. L. Perry "Barium-Cadmium Stabilization of Polyvinyl Chloride," Rubber Age 85 449-452 (June, 1959), and by H. Verity-Smith, British Plastics 27 176-179, 213-217, 307-311 (1954); the brochure by the same author The Development of the Organotin Stabilizer (Tin Research Institute, 1959) and the book La Stabilistion des Chlorures de Polyvinyle by F. Chevassus (Amphora, Paris, 1957).
Preponderant in quantity used for many years have been the lead salts, such as tribasic lead sulfate, normal and dibasic lead stearate, dibasic lead phthalate, dibasic leadphosphite, and basic lead carbonates and silicates. Vinyl chloride polymer compositions stabilized with lead compounds are recognized as outstanding in electical properties and good in color protection during long extended processing at high temperatures, while poor in clarity owing to the insolubility and pigmenting properties of the lead compounds. Next in quantity used have been the organic salt mixtures containing cadmium, as disclosed for example by W. Leistner, in U.S. Pat. No. 2,716,092 of Aug. 23, 1955, G. Mack in U.S. Pat. No. 2,935,491, of May 23, 1960 and J. Scullin in U.S. Pat. No. 3,390,112 of June 25, 1968. Cadmium containing stabilizers have provided excellent heat stability combined with outstanding clarity and resistance to weathering exposure. With the steady increase in usage of vinyl chloride polymer compositions and coincidentally increased concern about the accumulation of toxic materials in the human environment, there has developed a need to replace the lead and cadmium based stabilizers by environmentally more acceptable and no less effective stabilizers. The very favorable properties of the lead and cadmium containing stabilizers, however, have made it difficult to find equivalent replacements. In particular, vinyl chloride polymer compositions stabilized with materials other than lead and cadmium have been subject to objectionable yellowing even where the time to severe heat failure was relatively satisfactory.
J. Darby in U.S. Pat. No. 2,669,548 of Feb. 16, 1954 disclosed halogen-containing resin compositions having improved stability containing a mixture of a zinc salt and a calcium chelate derivative of a 1,3-dicarbonylic compound capable of keto-enol tautomerism. Zinc salts can be zinc salts of organic acids and zinc salts of weak inorganic acids, for example zinc acetate, zinc propionate, zinc octanoate, zinc ricinoleate stearate, and zinc salts of carbonic, silicic, and boric acids. Calcium chelates can be derivatives of betadiketones, betaketoacids, and the esters of betaketoacids, for example the calcium chelates of ethyl acetoacetate, phenyl acetoacetate, acetoacetic acid, acetylacetone, benzoylacetone, and diacetylacetone.
F. Ebel in U.S. Pat. 3,001,970 of Sept. 26, 1961 disclosed preventing the discoloration of polymers of vinylidene chloride in light by adding a small amount of a dibenzoylmethane of the general formula: ##STR3## in which R.sub.1 represents hydrogen or a hydroxyl radical, and R.sub.2, R.sub.3 and R.sub.4 represents hydrogen or hydrophobic radicals. Such hydrophobic radicals are for example alkyl, cycloalkyl, aryl, aralkyl and halogen radicals.
British Pat. No. 1,141,971 of May 23, 1967 to W. R. Grace & Co. disclosed zinc complexes of beta-dicarbonyl compounds used as stabilizing additives for chlorine-containing polymers in general, and polyvinyl chloride in particular. The zinc complexes possess the general formula: ##STR4## wherein R and R' are the same or different and are each hydrogen or an alkyl, alkoxy, phenyl or phenoxy group. Preferably when R represents an alkyl or alkoxy group, it contains 1 to 20 carbon atoms.
W. R. Pryer in U.S. Pat. No. 3,446,765 of May 27, 1969 disclosed that where unplasticized polyvinyl chloride compositions containing finely divided precipitated calcium carbonate discolor on exposure to light, one can prevent the discoloration by incorporating in the composition small amounts of basic compounds of metals, for example oxides of magnesium, zinc, and aluminum, particularly magnesium oxide. The only stabilizer present in a vinyl chloride polymer composition in which the favorable effect of the basic compound is demonstrated by Pryer is a barium/cadmium stabilizer.
L. Weisfeld in U.S. Pat. No. 3,493,536 of Feb. 3, 1970 disclosed that diaroylmethane compounds of the general formula C.sub.6 H.sub.5 CO--CHR--COC.sub.6 H.sub.5 wherein R is hydrogen or a monovalent hydrocarbon radical provide stabilizing action against the sensitizing effect of bismuth or antimony compounds on chlorine-containing materials.
C. E. Parks in Bristish Pat. No. 1,229,521 of Apr. 21, 1971 disclosed a synergistic combination of tin mercaptide stabilizers with calcium oxide, calcium phenoxide, calcium hydroxide and calcium alcoholates, whereby smaller amounts of tin mercaptide may be used with the synergist to obtain the same degree of heat stability as with much larger amounts of the tin mercaptide. In British Pat. No. 1,229,522 Parks disclosed a similar combination of tin mercaptide stabilizers with magnesium oxide or hydroxide, and noted that with other stabilizer systems, for example calcium zinc organic acid salts, the addition of magnesium oxide contributed to decreased heat stability when used in combination with the calcium-zinc stabilizer.
Similarly, T. Jennings in U.S. Pat. No. 3,764,571 of Oct. 9, 1973 disclosed a stabilizer combination for vinyl chloride polymers of a sulfur containing organotin compound having the structural feature ##STR5## with a metal carboxylic acid salt having the formula (RCXX)nM in which R is a hydrocarbon or substituted hydrocarbon radical, X is oxygen or sulfur, n is an integral number from 1-2 and M is an alkali or alkaline earth metal, and a basic compound which can be an alkali or alkaline earth (i.e. Group I and IIa) metal oxide, hydroxide, carbonate, bicarbonate, thiocarbonate, sulfide, bisulfide, sulfite or bisulfite.
Netherlands specification No. 7600213 of July 13, 1976 to Rhone Poulenc Industries disclosed the possibility of preventing the thermal breakdown of vinyl chloride polymers by adding 0.1 to 5% by weight of the polymer of one or more carboxylic acid salts of 2-valent metals such as calcium, barium, zinc, lead, or cadmium and 0.05 to 5% by weight of an organic compound having the formula: R.sub.1 --CO--CHR.sub.2 --CO--R.sub.3 in which R.sub.1 and R.sub.3, which can be alike or different, represent linear or branched alkyl or alkenyl groups with up to 30 carbon atoms, arylkyl groups with 7 to 36 carbon atoms, or aryl or cycloaliphatic groups with less than 14 carbon atoms, optionally substituted with halogen atoms, aryl or cycloaliphatic groups, methyl or ethyl groups; aliphatic R.sub.1 and R.sub.3 groups can also be modified by the presence of one or more --0--, ##STR6## or --CO-- groups, or taken together represent a 2-valent alkylene group having two to five carbon atoms; also, one of the groups R.sub.1 and R.sub.3 can be a hydrogen atom; R.sub.2 is a hydrogen atom, an alkyl or alkenyl group with up to 30 carbon atoms which can include --0--, ##STR7## and --CO-- groups, a group R--CO--R.sub.4 where R.sub.4 is an alkyl group with 1 to 30 carbon atoms or an aryl group when R.sub.1 and R.sub.3 are non-aromatic, or a group having the formula --R.sub.5 --CH(--CO--R.sub.1)--CO--R.sub.3 in which R.sub.5 is an alkylene group with 1 to 6 carbon atoms. The combination of carboxylic acid metal salt and 1,3-dicarbonyl compound is stated to be superior to an equimolar quantity of 1,3-dicarbonyl compound metal chelate.